The present invention relates to an image pickup apparatus, particularly to the image pickup apparatus with zooming function.
FIG. 1 shows a known image pickup apparatus capable of autofocusing with zooming function, which has an optical system 10 provided with a front lens section 1, a zoom lens section 2 and an imaging lens section 3.
A light beam depicted by an arrow A from an object is incident, via the optical system 10, to an image pickup device (such as a charge coupled device) 4 which converts the light beam to an electric signal. The signal is then applied to a camera circuit (not shown).
The electric signal is further applied, via a gain control circuit and a band pass filter and like, to a rectifier (all of them not shown) which picks up a specific high frequency component of the signal, and outputs the rectified high frequency component as a foucsing signal. When just-focusing, the focusing signal becomes maximum. The focusing signal is applied to an autofocusing (AF) circuit 5 which drives a motor 6 to slide the imaging lens section 3 to a just-focus point on an optical axis.
If further telephotographing is required, a conversion lens 17 for telephotographing should be attached in front of the front lens section 1.
Problems with the above apparatus are that attachment of the conversion lens to the apparatus takes time and if a conversion lens provided with more than two lenses is attached, the apparatus will become bulky. Further close-photographing under the telephotographing-mode will be impossible, if the conversion lens is attached.